This invention relates generally to optical recording channels and, more particularly, to improved systems and methods for splicing new data to existing data on optical recording media.
Data is stored on an optical disc in the form of microscopic pits (or marks) and lands (or spaces), which separate neighboring pits. As the optical disc spins, the pits and lands pass over an optical laser beam. The pits and lands of the disc reflect the laser beam at varying intensities. The reflected beam is then detected by an optical pick-up unit (OPU) and converted to a stream of binary data. Whenever the pick-up laser passes over a pit, a binary “0” is read. Whenever the pick-up laser passes over a land, a binary “1” is read. The resulting system of encoded channel data is then converted to user data by a series of decoding steps.
Most writable optical discs (e.g., CD, DVD, HD-DVD, and Blu-Ray discs) have grooves formed along spiral or concentric tracks. A specific variation may be applied to the wall of each groove in a groove formation process. A specific frequency may then be generated based on the specific variation in a recording/reproduction process. The specific frequency may be used as an auxiliary clock source, whereby the specific frequency is called a wobble signal.
Timing control and location information are maintained with the help of the wobble signals, and, in the case of DVD-R(W) media, land pre-pit signals. For example, when writing to an optical disc, the timing loop may be locked to a disc wobble signal. The wobble signal may also contain address information. Traditionally, during a write process, the timing lock on the wobble signal is maintained and the address information is monitored.
In some cases, however, new data may need to be abutted to a previously-recorded set of data on an optical disc. For example, using multi-session recording, each track of data is typically recorded in a single session, which is closed after the track is recorded. A lead-out may be written to the disc after the session is closed, and a lead-in may be written, which prepares the disc for a new session to be written in the future. As another example, a user may wish to incrementally add data to an existing track (e.g., using packet writing or any other suitable incremental writing technique), or some system interrupt (e.g., an empty write buffer or system distortion) may halt the writing process. At some later time, a user may wish to write more data to the disc so that it appears the old data and the new data were written in one sequence. The boundary between the set of previously-recorded data and the new data is called a write splice.
However, a write splice often appears as a phase jump to the optical read channel. This could result in a temporary loss of timing lock and data read errors. There are at least two reasons why a write splice may manifest itself as a phase jump. First, the timing loop phase with respect to the disc position may be different between the end of the first write and the beginning of the second write.
Second, the write path delay may vary between the first write session and the second write session, or the write path delay compensation may not be correctly calibrated. Since distortion in optical recording channels is highly volatile, there may be a great variation in timing loop jitter. For example, laser power may be pulsating during a write operation, but not during a read operation. This may result in drastically different values of jitter during the two operations. Therefore, locking to a wobble signal while tracking over a previously written portion of the disc is far from ideal when writing or splicing data.
Accordingly, it is desirable to provide systems and methods for improved splicing of data in optical channels. The improved write splice may reduce the phase jump in the read back signal at the write splice location. It is also desirable to provide systems and methods for improved write splices using both recordable (R) and rewritable (RW) optical media.